The invention relates to a method of towing sources of seismic energy behind a vessel, especially in seismic surveys in waters that are covered with ice, with a source of energy or arrays of sources of energy being suspended from buoyancy means which are towed behind the vessel. The invention also relates to an arrangement for use in the method.
When seismic surveys are carried out in waters that are covered with ice, other kinds of problems arise than those commonly encountered in seismic surveys at sea. Such problems are mainly caused by the ice and the noise generated by ice being broken up when the towing vessel is propulsed in order to permit seismic surveys to be made. Icebreaking causes noise of such a level that the seismic signals are no longer detectable in the streamer cable. These problems are avoided by carrying out measurements as disclosed in NO Patent Application Norwegian 90 1616 by the same applicant. Another problem prevailing in seismic surveys in waters which are covered with ice is connected with towing the sources of seismic energy. The sources of seismic energy which are towed behind the vessel are suspended on some kind of buoyancy means which maintain a plurality of sources of energy at a predetermined mutual distance in order to permit the sources together to emit a seismic impulse which is defined in the desired manner and is detected by the hydrophones of the streamer cable. In waters which are covered with ice, however, the buoyancy means for the sources of energy will be influenced by broken ice, which may partly damage them, but at least will cause interference of their advance. Ice may pile up in front of the buoyancy means and may hamper advance. Under the surface of the water such a pile-up may also disturb the suspension lines of the sources of energy, so that the latter are displaced from their correct position. Consequently, the seismic signals may be distorted and, thus, render recordings dubious.